U.S. Defense Secretary Chuck Hagel says it would be a mistake for the United States to turn to isolationism to avoid involvement in the world's conflicts.

After 13 years of U.S.-led wars in Iraq and Afghanistan, Hagel told a foreign affairs forum Tuesday in Chicago that Americans are increasingly skeptical of foreign military engagements.

But he said it would be "a mistake to view our global responsibilities as a burden or charity." He said failure to engage in world affairs would prove costly.

"Turning inward, history teaches us, does not insulate us from the world's troubles. It only forces us to be more engaged later -- at a higher cost, at a higher cost in blood and treasure, and often on the terms of others," said Hagel.

He said "terrorists and insurgents are not fading into oblivion," and that is one reason the United States is increasing its spending on special operations forces.